Takeshi Kijima

Improvement in D-E Hysteresis Curve Squareness of PZT Thin Films—Effect of Oxygen Partial Pressure in High-Pressure Post-Annealing

A high-pressure annealing was applied to a post-annealing process for sol-gel derived PZT thin films. The squareness of D-E hysteresis curves changes depending on both total pressure and oxygen concentration. Moreover, the change follows the product of the total pressure and the oxygen concentration, which correspond to oxygen partial pressure PO2. Where the PO2 is higher than 0.03 MPa, few of the squareness of the hysteresis curve are excellent. The squareness of the hysteresis curves dramatically improve as the PO2 decreases. Where the PO2 is lower than 0.01 MPa, the squareness deteriorates slightly. These changes in the D-E hysteresis curves are thought to be explained by the generation of lead and oxygen vacancies as a function of the PO2.

New low temperature preparation of ferroelectric Bi4Ti3O12 thin films by MOCVD method

Abstract Pt/Bi4Ti3O12(001)/Bi2SiO5(100)/Si(100) structures have been fabricated by the metal-organic chemical vapor deposition (MOCVD) at 500°C. Bi2SiO5 film is used as a buffer layer to grow ferroelectric Bi4Ti3O12 films because of its relatively high dielectric constant (∊r=30). The memory window has a C-V characteristic of about 0.8 V, and the retention time estimated by the zero-bias capacitance for the Pt/100-nm-Bi4Ti3O12/30-nm-Bi2SiO5/Si/Al structure is more than 11 days.

Orientation Control of (Bi,La) 4 Ti 3 O 12 Thin Films by Addition of Silicates and Germanates

Orientation of crystallites in (Bi,La) 4 Ti 3 O 12 (BLT) thin films were successfully controlled by adding such silicates and germanates as Bi 2 SiO 5 , ZrSiO 4 and La 2 GeO 5 . The ferroelectric films were formed by spin-coating mixed sol-gel solutions of BLT and silicate or germanate on a Pt/Ti/SiO 2 /Si structure. It was found from XRD analysis that the preferred orientation of crystallites in the BLT films was changed by the additives. That is, the orientation of crystallites in a Bi 2 SiO 5 -added BLT film was random, while it was almost perfectly c-axis-oriented in La 2 GeO 5 -added BLT and it was strongly (117)-oriented when ZrSiO 4 was added to BLT. It was also found that the remnant polarization and coercive field changed reflecting these different orientations.

Ferroelectric Random Access Memory Using Pb(Zr,Ti,Nb)O 3 Films

We have succeeded in fabricating Pb(Zr,Ti,Nb)O3 (PZTN) thin films with 20-atomic% Nb at B site in ABO3 structure, which was suitable for high density and reliable ferroelectric random access memory (FeRAM). A sol-gel spin-coating method was used to prepare the PZTN thin films. 1 mol% Si co-doping was applied to promote the solid-solution of Nb atom into the original Pb(Zr,Ti)O3 films. We suggested that in our PZTN the oxygen vacancies were well suppressed due to Nb substitution comparing with conventional Pb(Zr,Ti)O3 (PZT). We also succeeded in obtaining excellent electric properties in 1times1 mum2 capacitors with PZTN. In addition, we confirmed the no data degradation and the high reliability of our PZTN material has been demonstrated by 64 k-bits FeRAM chip operation.

Fabrication and Characterization of Lead Silicate Doped PZT Thin Films

The crystal structure, surface morphology and electrical properties of PbSiO x (PSO) doped Pb(Zr,Ti)O 3 (PZT) thin films were systematically investigated. The starting solutions of PSO-doped PZT were prepared by mixing sol-gel solutions of PZT and PSO. RTA-calcined thin films were crystallized by means of an oxygen partial pressure controlled post-annealing process. After the calcining process, lightly doped PZT thin films containing an amount of PSO dopant less than 1.0 at.% exhibit (111)-preferred orientation, and fine grains having a diameter of 50 nm and column-like structure. As the amount of PSO dopant is increased to 5.0 at.%, the (111) peaks becomes obscure and the (100) peaks together with the minor (110) peaks becomes dominant. The column-like structure changes into a plate-like structure having coarse grains whose diameter exceeds 500 nm. Further increasing the level of PSO dopant to 20.0 at.% causes the appearance of a pyrochlore phase having an extremely smooth surface without apparent grains. On the other hand, after the post-annealing process, the pyrochlore phase seen in the heavily doped PZT remarkably disappears, replaced by a perovskite phase together with PSO. The remnant polarization (Pr) gradually decreases as the amount of PSO dopant increases. The break down voltage, fatigue, imprint and other reliability parameters are improved within the proper doping range.